<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title>denglu</title>
</head>
<body>
<div class="login-box">
  <h2>Login</h2>
  <form>
    <div class="user-box">
      <input type="text" name="" required>
      <label>Username</label>
    </div>
    <div class="user-box">
      <input type="password" name="" required>
      <label>Password</label>
    </div>
    <a href="#">
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      Submit
    </a>
  </form>
</div>
</body>
</html>
<style type="text/css">
html {
  height: 100%;
}
body {
  margin:0;
  padding:0;
  font-family: sans-serif;
  animation:myfirst 3s infinite alternate;
}
h2:hover{
  text-shadow:0 0 20px #FF00FF ,
              0 0 50px #FF00FF  ,
              0 0 75px #FF00FF  ,
              0 0 100px #FF00FF 
}
.login-box {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 400px;
  padding: 40px;
  transform: translate(-50%, -50%);
  background:MediumVioletRed;
  box-sizing: border-box;
  box-shadow: 0 15px 25px rgba(0,0,0,.6);
  border-radius: 10px;
}
.login-box h2 {
  margin: 0 0 30px;
  padding: 0;
  color: #fff;
  text-align: center;

}
.login-box .user-box {
  position: relative;
}

.login-box .user-box input {
  width: 100%;
  padding: 10px 0;
  font-size: 16px;
  color: #fff;
  margin-bottom: 30px;
  border: none;
  border-bottom: 1px solid #fff;
  outline: none;
  background: transparent;
}
@keyframes myfirst
{
0%   {background:#FF1493}
50%  {background:#C71585}
100%  {background:#FF69B4}
}
.login-box .user-box label {
  position: absolute;
  top:0;
  left: 0;
  padding: 10px 0;
  font-size: 16px;
  color: #fff;
  pointer-events: none;
  transition: .5s;
}

.login-box .user-box input:focus ~ label,
.login-box .user-box input:valid ~ label {
  top: 0px;
  left: 0px;
  color: #03e9f4;
  font-size: 25px;
  text-opacity：0.25
}

.login-box form a {
  position: relative;
  display: inline-block;
  padding: 10px 20px;
  color: ghostwhite;
  font-size: 16px;
  text-decoration: none;
  text-transform: uppercase;
  overflow: hidden;
  transition: .5s;
  margin-top: 40px;
  letter-spacing: 4px
}

.login-box a:hover {
  background:#FF69B4;
  color: #fff;
  border-radius: 5px #FF69B4;
  box-shadow: 0 0 5px #FF69B4,
              0 0 25px #FF69B4 ,
              0 0 50px #FF69B4,
              0 0 100px #FF69B4 ;
}

.login-box a span {
  position: absolute;
  display: block;
}

.login-box a span:nth-child(1) {
  top: 0;
  
  width: 100%;
  height: 2px;
  background: linear-gradient(90deg, transparent, #FF69B4);
  animation: btn-anim1 1s linear infinite;
}

@keyframes btn-anim1 {
  0% {
    left: -100%;
  }
  50%,100% {
    left: 100%;
  }
}

.login-box a span:nth-child(2) {
  top: -100%;
  right: 0;
  width: 2px;
  height: 100%;
  background: linear-gradient(180deg, transparent,#FF69B4);
  animation: btn-anim2 1s linear infinite;
  animation-delay: .25s
}

@keyframes btn-anim2 {
  0% {
    top: -100%;
  }
  50%,100% {
    top: 100%;
  }
}

.login-box a span:nth-child(3) {
  bottom: 0;
  right: -100%;
  width: 100%;
  height: 2px;
  background: linear-gradient(270deg, transparent,#FF69B4);
  animation: btn-anim3 1s linear infinite;
  animation-delay: .5s
}

@keyframes btn-anim3 {
  0% {
    right: -100%;
  }
  50%,100% {
    right: 100%;
  }
}

.login-box a span:nth-child(4) {
  bottom: -100%;
  left: 0;
  width: 2px;
  height: 100%;
  background: linear-gradient(360deg, transparent, #FF69B4);
  animation: btn-anim4 1s linear infinite;
  animation-delay: .75s
}

@keyframes btn-anim4 {
  0% {
    bottom: -100%;
  }
  50%,100% {
    bottom: 100%;
  }
}
	
</style>